Two-party line telephone system



May 14, 1935. e. DEAKIN 2,001,095

TWO-PARTY LINE TELEPHONE SYSTEM Filed April 27. less I FIG! 3 v T u L9 a ,5 I a6 l0 4 7 E 3 as INVENTOR GERALD DEAKIN TTORNEY talkingto a .called line.

by any operation which may Patented May 14, 1935 k c c 23101 095 HmWo-BAR Y LINE TELEPHONE SYSTEM team Dakin, New York; N.,Y.,rassighor', b& mesne assignments, to Western Electric Company, Incorporated, New York, N. Y., a corpo situates A ulet, 193s ,seria11sio;;668,1:9 t tw g -15- 7 j A t bases and to the contacts 20 and 2| or the ter- This invention relates' to two party line auto,- matic telephone systems. l .h r

. One object of theinvention isto provide a two party line system wherein one party cannot be interfered with during dialling or conversation be performed by the other party on the sameline. jEfiQh'gTSfifliiiOh is provided with an asymmetricdevice; suchas a rectifier of the dry type, and the rectifiers are COIL:- nected in such a manner that when oneyparty7s telephone is in use, no currentcanmfiow. through the dial lswitch contacts ortransmitter-of the telephone ofthe other party.

A f ther object of the invention is to provide a system ofthe above mentioned type wherein the service is secret, so that one party cannot listen in to the conversation while the other .party is A further object of the invention relates to the provision of meansj whereby either one. of the two parties can call and talk with the other by way of the central ofiice.

Referring to the drawing, Figure 1 shows, the circuitsof the two party line st'ations and certain connections at the central oflice. Figure 2 shows a modified circuit fora subscribersstation to be used when secrecy is desired and Figure 3 shows a subscriber's circuit which may be employed for revertive calling. i I

InFigure 1, the circuits shown forjstations A and Bareidentical except for their connection to the lines a, 1) connecting the stations to the central ofiice C. In station A, current passes from line 12 through rectifier l, dial contacts 2, transmitter 3, switch hook contact 4, winding 5 of induction coil 6 back to line a. The receiver I is associated with this circuit by the winding 8 of induction coil 6 and condenser 9 and also by switch hook contact If]. The ringer H is connected to the circuit as shown and to earth.

' In the circuit for station B, current must be received over line a, as the rectifier I is connected in such a way as to prevent the passage of current therethrough when the current arrives over line b. Winding 5 of the induction coil 6 is connected to line 17 instead of line a as was the case with station A.

At the central office C, the lines a and In her-- minate at terminal I2 for party A at contacts l3 and M respectively and at terminal [5 forparty B at contacts 5 and I! respectively. Line relay 40 serves for party A, its winding connected to negative battery beingalso connected through contact l8 of cut-off relay l9 to line a. The winding of cut-off relaylS is connected to negative minals 12 and l5respectivelyh r r i Line :relay 22- serves Ior party 3, its winding being connected' tonegative battery on theone hand, and through contact -.23 of cut-ofi relay I 9 to line b on the other hand. 3 Test contact-.24 of terminal I2 is adapted to be connected to.-n.egative battery 25 through resistances' 2t}v contact 21 of line relay 22 when the latter. isg-deenergized; and contact 28 when line relayl! is energized, Testcontact 29 of terminal I5, is adapted to be connected to negative when relay 22 is energized. A i

servicemeters Hand 32-, whose windings are connected'to negative-"battery and to contacts 33 and34 of terminals l2 and ,l 5 respectively, are also providecL i 1 g When party -l l .lifts.the receiver tomake a call, acircuit is completed fromgroun-d, ringer l l,

' battery 25; through resistance 26 at contact 39 winding 8., receiver, 1, contacts lllan dr l; winding 5,-linea, contact l8, winding ofline: relay; l-i to negative battery. Line relay I "I operates and placesatest potentialfon contact24. l

' Line relay 22 cannot operate because its circuit isblocked at the rectifier l of station A.-

The slifting of the receiveralso causes aline finder (not shown)v to operate in the well known manner, and thisfindenselectsthe terminal I2 .byreason of-the test potential having been applied to @contact' 24'. A connecting; circuit (not shown) now selects this line finder and connects a current supply bridge (not shown)' to the line, negative potential being connected to line a, and positive potential to line b. Cut-off relay [9 now operates in the well known manner breaking the circuits of line relays H and 22 (this relay has not operated) at contacts J8 and 23 respectively. Current now flows from the current bridge through the circuit of station A, but cannot fiow through the circuit of station B in the event the receiver at station B is lifted, because it is blocked. at rectifier I at that station. The operation for station B is similar to the above, except that in this case the current bridge is oppositely connected, so that positive potential is now on the a line and current can pass well known manner to the exclusion of the service meter of the other station which has not initiated the call.

twee There being no completed circuit through the apparatus at station B when station A is calling, it is clear that the party at station B cannot interfere, although he may remove his receiver and operate his dial.

In the case of a call incoming from another line, positive potential will be. placed on the 17 line if the call is for station A, whereas if the call is for station B, positive potential will be placed on the a line. Ringing current for station A is applied to the 1) line and for station B to the a line.

In the arrangement just described, when station A is involved in a call, it will be. possible for the party at station B to remove his receiver and listen in to the conversation. In Figure 2 a circuit for the subscribers station is shown which will make it impossible for the other party to even listen in. The same reference characters are used in this figure as were used in Figure 1, so tar as the apparatus common to both are concerned. Instead of the direct connection between rectifier I and line b as was the case of station A, Figure 1, the current now passes through the winding of relay 35.

Condenser 36 is provided to pennitthe talking path from line b to reach the transmitter 3 without passing through the winding of relay 3! and rectifier I. Contact 31', normally closed, forms a short circuit around receiver 1, so that the latter cannot become operative until relay 36 has been energized and contact 31 opened.

If it is desired to provide for revertive calling, the arrangement or Figure 3 may be used. Here a member 38 is-provided so that in the case where relay 35 has been energized, and contact 3'! opened, this member 38 will, upon the receiver 1 being lifted, mechanically hold contact 31 open. If relay i6 is not energized, the removal of the receiver 1 will not afiect the annafture of relay 35 in any way and such armature will be free to move thereafter in case relay 35 becomes energised, whereupon member I! then mechanically holds it. The operation of relay 35 in this case will also place a short circuit around the rectifier I at contact 39.

Assuming that station a is calling station B, it will be clear that the initial operation at station A is similar to that as in Figure l or 2, and as member 38 holds contact 31 open, the current can then be reversed at the central ofilce as is the usual procedure in making such revertive calls, and the normal operation will take place at station B.

What is claimed is:

1. A two party automatic telephone exchange system comprising a rectifier at each station, aline circuit, a service meter individual to each station and located at the central office, and means including a finder switch for each station whereby only the service meter individual to one of said stations is adapted to be associated with the line circuit when said station originates a call.

2. A two party line forming a part of an automatic telephone exchange system, two subscribers stations associated with said line, means including a'rectiiier at each station for rendering it inoperative when the other station is involved in a call with another party in the system, and means for disabling said rectifier means to permit one of said two subscribers stations to call and converse with the other of said two subscribers stations.

3. In a subscribers circuit arrangement for a two party line, a receiver, a rectifier in series with a relay, a short circuit normally maintained about said receiver but adapted to be broken upon the passage of current through said rectifier and relay.

4. In a subscribers circuit arrangement for a two party line a switch hook, a receiver, a rectifier, a relay having an armature adapted to break a short circuit about said receiver upon the energization of said relay by current passing through said rectifier, and means associated with said switch hook for maintaining said armature in its operated position after current ceases to flow through said relay.

5. In a. subscriber's circuit arrangement for a two party line means comprising a rectifier for isolating said circuit and means under the control of the subscriber for disabling said first mentioned means in the case of a revertive call when the line is otherwise free.

6. In a circuit arrangement for a subscribers station for a two party line comprising in com bination a receiver, a rectifier and a relay, said relay being adapted to control separate short circuits about said receiver and said rectifier.

GERALD DEAKIN. 

